This invention relates to inspecting glass containers for the specific defect or presence of "fused" or "stuck" particles of glass within the interior of the container and in particular, fused or stuck glass which is adhering to the interior bottom surface of the glass container.
In the manufacture of glassware, and in particular glass containers, occasionally a piece of glass which may originate at some other location within the glass plant, will find its way to the area where the containers are being either formed or handled after forming prior to being packed into shipping cartons. It should be understood that in almost any glass plant there is always the possibility that breakage will occur on the production line at various points along the line which might cause small pieces of glass to fly into or become enclosed in a newly formed glass container. When this occurs, at the time the glass is in a relatively hot state, it is very possible for the small piece of glass to become fused to the inner bottom surface of the glass container. It should be kept in mind that glass becomes soft and would fuse if the interfacial temperature were to approximate 800.degree. between the glass particle and the interior bottom of the glass container. The container, after it is newly formed and set out on a dead plate or on the machine conveyor which moves the containers away from the forming machine, may have a sufficient temperature such that it will cause small particles of broken glass to adhere to the interior thereof. Thus, even if the containers, at some later time prior to packing, are swept with compressed air or are inverted, these small particles of glass will still adhere to the interior thereof.
It is desirable not to ship containers that might have stuck glass therein and for this reason, the present invention has as its principal object the selection and examination of glass containers, after they have been annealed, to determine the presence or absence of any fused glass that might be adhering to the interior thereof. While the invention may find its principal utility in determining fused or stuck glass in what are termed "wide mouth" containers, such as baby food jars, home canning jars, it will have equal utility when being used for inspecting tumblers or other hollow glass articles that can be illuminated from the bottom while being rotated about their vertical axis and positioned beneath an annular array of solar cells.
It has been known in the prior art to illuminate containers from below and to then examine the containers through the open upper mouth or finish area thereof. In most of these "prior art" types of inspection devices, it is important or necessary that the light source beneath the container be of a diffuse character so that mold marks or molded-in lettering which appears on the bottom of glass containers not give the appearance of a defect to the optical pick-up. Since most optical inspection apparatus for glass containers are looking for defects of the reflecting type, defects which will deflect (reflect or refract) light out of a projected direction, raised lettering will either make the image of the bottom of the bottle appear to have dark spots due to the reflection or refraction of the light.
It has also been the practice in the art to shine a light through the finish of the container and have it sweep the inner diameter of the bottom of the container, for example, as shown in U.S. Pat. No. 3,356,853. In this particular patent, however, the bottom wall of the hollow transparent container is being inspected for those types of defects that will cause a focused beam of light to be reflected or refracted out of the normal direction that it is taking from the source. It has also been known to inspect glass containers with the use of a laser beam as the light source and the light piping characteristics or internal reflections of the container wall have been utilized as a phenomenon in order to provide a means for illuminating reflecting type defects. Scanning the exterior of a laser illuminated sidewall of a container with a photo-sensitive pickup has been used to determine the reflectance of light out of the wall of the container due to a defect. Such defects are known as checks, stones or blisters appearing within the wall of the container. The use of a laser beam as a light source in the manner suggested above, may be found in U.S. Pat. No. 3,302,786 of common assignee with the present application.